1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of mixed fatty-acid esters using zeolitic adsorbents. More specifically the invention relates to a process for separating an ester of a polyethanoid fatty acid and an ester of a monoethanoid fatty acid which process employs a first zeolitic adsorbent which selectively adsorbs an ester of a polyethanoid fatty acid and a second zeolitic adsorbent which selectively adsorbs an ester of a monoethanoid fatty acid.
2. Description of the Prior Art
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon types from mixtures thereof. As a few examples, a separation process disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491 uses a type A zeolite to separate normal paraffins from branched-chain paraffins and processes described in U.S. Pat. Nos. 3,265,750 and 3,510,423 use type X or type Y zeolites to separate olefinic hydrocarbons from paraffinic hydrocarbons. In addition to their use in processes for separating hydrocarbon types, X and Y zeolites have been employed in processes to separate individual hydrocarbon isomers. As a few examples, adsorbents comprising X and Y zeolites are used in the process described in U.S. Pat. No. 3,114,782 to separate alkyl-trisubstituted benzene isomers; in the process described in U.S. Pat. No. 3,864,416 to separate alkyl-tetrasubstituted monocyclic aromatic isomers; in the process described in U.S. Pat. No. 3,668,267 to separate specific alkyl-substituted naphthalenes. Because of the commercial importance of para-xylene, perhaps the more well-known and extensively used hydrocarbon isomer separation processes are those for separating para-xylene from a mixture of C.sub.8 aromatics. In processes described in U.S. Pat. Nos. 3,558,730; 3,558,732; 3,626,020; 3,663,638; and 3,734,974 for example adsorbents comprising particular zeolites are used to separate para-xylene from feed mixtures comprising para-xylene and at least one other xylene isomer by selectively adsorbing para-xylene over the other xylene isomers.
In contrast, our invention relates to the separation of non-hydrocarbons and more specifically to the separation of mixed fatty-acid esters. We have discovered that a first adsorbent comprising a X or a Y zeolite containing certain selected cations at the exchangeable cationic sites exhibits higher adsorptive selectivity for an ester of a polyethanoid fatty acid than for either an ester of a monoethanoid fatty acid or an ester of a saturated fatty acid and that a second adsorbent comprising an X or a Y zeolite containing certain selected cations at the exchangeable cationic sites exhibits adsorptive selectivity for a monoethanoid fatty acid with respect to an ester of a saturated fatty acid thereby making separation of an ester of a polyethanoid fatty acid and an ester of a monoethanoid fatty acid by solid-bed selective adsorption possible. In a specific embodiment our process is a process for separating the polyethanoid fatty-acid ester methyl linoleate and the monoethanoid fatty-acid ester methyl oleate from a mixture comprising methyl linoleate, methyl oleate and the saturated fatty-acid ester methyl palmitate or methyl stearate or mixtures of the two.
Production of fatty esters is the most important phase in the industrial chemistry of fatty acids. The esters produced are of several types and include those resulting from the reaction of fatty acids with monohydric alcohols, polyhydric alcohols, ethylene or propylene oxide, and acetylene or vinyl acetate. The principal monohydric alcohols are methanol, 1-propanol, 2-propanol and 1-butanol. The greatest uses of fatty-acid esters in general are in the solvent and plastizicer fields. Esters of monohydric alcohols are used for plasticizers and in cosmetics. Esters of saturated fatty acids are of value in compounding lubricating oil, as a lubricant for the textile and molding trade, in special lacquers, as a waterproofing agent, and in the cosmetic and pharmaceutical fields. Esters of unsaturated fatty acids find use as drying agents.